1. Field of the Invention
This invention relates to improvements in or relating to apparatus for forming a linear, elongated object, or more specifically an elongated electric conductor used with transformers, reactors, electric induction furnaces, etc., into cylindrical coils.
2. Description of the Prior Art
Generally, coils used with transformers, electric induction furnaces, etc. are formed by shaping a linear, elongated conductor into loops of the coils and winding same in cylindrical form. Processes for forming coils include a hot bending process and a cold bending process. In the hot bending process, a linear, elongated conductor is heated and annealed, directly wound into a coil on a winding pattern with a strong force and struck with a hammer to apply pressure thereto so as to correct the diameter of the coil. In the cold winding process, a linear elongated conductor is continuously bent by means of a bender to form a coil of a cylindrical shape. The former process is low in operation efficiency because correction of the diameter of a coil to a predetermined value is effected by hammering. Thus the latter process is generally in use nowadays.
FIG. 1 shows one example of the coil winding apparatus for carrying the cold bending process into practice. As shown, a linear, elongated conductor 1 is fed at a constant velocity in a direction a toward a bending roller assembly 6 by means of pinch rollers 4 and 5 of a conductor feeding device 3 mounted on base 1. The linear conductor 1 fed in this way is continuously bent by bending rollers 7, 8 and 9 of the bending roller assembly 6 into loops 10 and shaped into a cylindrical coil 12 shown in FIG. 2. In this apparatus, the bending rollers 7 and 9 are rotated in a direction b in synchronism with the movement of the linear conductor 1 which is fed in the direction a, while the bending roller 8 is permitted to rotate freely in a direction c and to move in a direction e, so that the linear conductor 1 can be held between the bending rollers 7 and 9 on the one hand and the bending roller 8 on the other hand. Thus the linear conductor 1 is continuously bent into the loops 10 by moving the bending roller 8 in the direction e to form the loops 10 of the cylindrical coil 12. Each loop 10 of the coil 12 falls downwardly by its own weight on to a rotary table 14 of a winding device 13, the rotary table 14 being rotated in a direction g in synchronism with the movement of the loop 10 of the coil 12 which is fed in a direction f and at the same time moved downwardly in accordance with the distance covered by the downward movement of the loops 10 of the coil 12. Thus the linear conductor 1 can be continuously formed into the loops 10 by means of the bending roller assembly 6 to produce the cylindrical coil 12.
Some disadvantages are associated with the coil winding apparatus shown in FIGS. 1 and 2. They are as follows:
1. The loops 10 of the cylindrical coil 12 are formed by continuously bending the linear conductor 1 by means of the bending rollers 7, 8 and 9 solely by relying on the resilience of the material of the conductor 1, so that the loops 10 may vary from one another in diameter and shape and have different diameters d.sub.1, d.sub.2 and d.sub.3, for example. Usually, allowable tolerances of the diameter of the loops of a coil must fall within the limits of .+-. 3 mm, but the loops 10 of the coil 12 produced by this apparatus differ from one another in diameter such that the difference in value range from .+-. 5 mm to .+-. 10 mm.
2. As the operation of winding the coil 12 progresses, the loops 10 formed by bending the linear conductor 1 by means of the bending roller assembly 6 vary from one another in diameter, with the result that the loops 10 extend alternately to right and left in zigzag form as shown in FIG. 2. This makes it impossible to produce the cylindrical coil 12 which stands upright on the rotary table 14.